In the field of marine seismic exploration, it is important to determine the configuration of the rock strata underlying the subsea earth's surface to locate subsurface structures favorable to the accumulation of oil and gas. In marine seismic surveying, this is accomplished by generating acoustic pulses or shock waves with sound sources, such as air guns, and by monitoring the resultant acoustic waves which reflect off the subsea interfaces with acoustic sensors. In a typical marine surveying operation, the seismic sound sources and the acoustic sensors are towed in designated patterns behind a seismic vessel. The basic principles of these surveying operations are well known to those skilled in the art.
Commonly, an array of seismic acoustic sensors, such as hydrophones, are configured in a seismic cable where the hydrophones are spaced along the length of the seismic cable. This seismic cable typically is called a streamer or streamer cable. The streamers are connected to apparatus on the vessel which includes the power source and the data control system.
To optimally develop 3-D marine surveys, to reduce the number of passes required of the seismic vessel in surveying a specific area and to improve the quality of the resulting geophysical information, multiple streamer cables typically are deployed in a pattern parallel to the centerline of the vessel. The streamer cables are separated from each other by calculated offset distances to provide the desired, spaced parallel pathways which minimize duplicate coverage but are adequate to cover the area to be surveyed. To obtain and maintain the desired lateral distances between adjacent streamer cables throughout the time period during which the seismic vessel is traversing the survey area, the streamer cables are attached at predetermined tow points on the cable to devices referred in the art of seismic exploration as pullavanes or para-vanes. The para-vanes are towed to the side of the vessel and provide the means to tow the streamer cables along pathways parallel to but laterally spaced from the pathway of the towing vessel.
The streamer cable typically is filled with a fluid which acts as a buoyancy material to keep the streamer cable at the desired depth beneath the surface of the water during the surveying operation. Because of the length of the streamers (sometimes several miles/kms in length), the streamers are in danger of colliding with other vessels. Therefore, a floatation device, such as a tail buoy, is attached to the submerged, tail end of the streamer to provide means to visibly approximate the location of the end of the streamer cable. The tail buoy is also quite useful for retrieval operations. If the vessel-end of the marine cable becomes detached from the vessel, the marine cable can be retrieved from the tail buoy end of the cable by using the tow line attached to the tail buoy and the streamer.
Additionally, the tail buoy commonly contains equipment for receiving data from a positioning system, such as the satellite navigation system known as the Global Positioning System (GPS), processing the data and transmitting the tail buoy's position information to a tracking system on the vessel. The tail buoy's positioning data not only provides a means to physically locate the tail buoy but can also be used to assist in determining the actual position of the end of the streamer cable. Increased accuracy in the calculated position of end of the streamer cable, and thereby increased accuracy for the positions of the acoustic sensors in the streamer cable, provides for increased precision in correlating the seismic signals received by the acoustic sensors to actual earth formations.
Various devices through the streamer require electricity to operate. This electricity is primarily provided from the vessel through the streamer and/or through batteries. Typically the equipment utilized for positioning the streamers and other spread elements such as the seismic source and tail buoys equipped with GPS has been batteries.
It is therefore a desire to provide an in-sea power generator for providing a source of electricity to the in-sea equipment. It is a still further desire to provide an in-sea power generation that is not propeller driven or provided by solar energy.